Orthopedic surgical procedures for knee meniscus replacement have improved over the years, concurrent with improvements in surgical instruments, expertise, and suitable materials. Although some injuries to a meniscus may be repaired, symptomatic biomechanical loss of meniscal function may indicate the need for a meniscal replacement procedure.
Each knee has two menisci, a lateral and a medial meniscus. Each meniscus is a crescent-shaped fibrocartilaginous tissue primarily attached to the tibial bone at an anterior and a posterior horn. The menisci deepen and cushion the receiving area of the tibia, into which two condyles of the femur transfer the weight of the erect human body. The meniscus acts to increase the contact area, provide cushion at impact and may play a role in articular cartilage nutrition.
Meniscus transplantation has become a commonly offered option for patients experiencing symptoms secondary to the absence of meniscus. One goal of the present meniscus transplantation invention is to improve the efficiency of the surgery, and maintain reproducibility and quality. Another goal, to assist in this allograft technique, is to provide a system of instruments to assist in position planning followed by fixation.
Recently one supplier of allograph tissue obtained from cadaver donation, Regeneration Technologies, Inc., has offered pre-sized meniscus allografts. Review of the limited meniscal allograft basic science literature suggests that soft tissue fixation alone is sub-optimal, and that bony fixation appears to assist in reduplication of hoop stresses. This reduplication of the biomechanical effects of a meniscus is essential to restore function. The allografts available from Regeneration Technologies have the capability of use for bone bridge and bone plug techniques. The bone plug technique is well described in the literature, and the present invention introduces new modifications to the bone bridge concept.
The present invention relates to an innovative procedure, system, kits, and related instruments, for the replacement of a knee meniscus using an allograft or xenograft meniscus, connected to a bone section, obtained from a donor. One reason for development of this invention is that, despite realized advantages from existing methods, there have been some difficulties encountered with utilizing meniscus implants. For example, surgical procedures involving transplantation and fixation of these implants can be tedious and lengthy. Currently, the bones involved in meniscus replacement surgery must be specifically shaped for the recipient during surgery. This can require up to or over an hour of surgical time.
Two common approaches to meniscus replacement are the keyhole surgical technique and the double bone plug technique. The keyhole technique uses a keyhole guide having a posteriorly placed pin to establish an orientation for a guide pin. The pin is driven into the anterior face of the tibia, and a reamer is used to drill out bone around this pin, forming the wider area of the keyhole. In this method, fluoroscopy could be used to verify that the pin lies parallel to the tibial plateau. That is rarely the practice. However, there is no direct visual method to ascertain correct placement when using this approach. Next, a ronguer or burr is used to open a slot to the top of the tibia to complete the keyhole-shaped slot. In subsequent steps, allograft or xenograft tissue comprising bone attached to a replacement meniscus is shaped so the bone fits the keyhole. This may require considerable crafting during the surgical period, and because of the need to custom-fit the implant to the surgically created keyhole, the implant generally cannot be fashioned to a precise fit prior to initiation of the surgical procedure. Once shaped to fit the keyhole, this tissue is slid into place in the tibia, and the operation is concluded.
For the double bone plug technique, the bone attaching to the anterior and posterior meniscus horn attachments are shaped into circular bone plugs. A guide, such as an ACL guide, is used to position the posterior hole socket in the tibia to receive the posterior plug. The posterior plug is secured into this socket, the graft is positioned, and a hole is made for the anterior plug. The anterior plug then is secured in place, and the operation is concluded.
In both of the above techniques, the surgical team is required to make substantial modifications to the xenograft or allograft implant to custom fit it to the particular recipient""s requirements. Despite this often-substantial effort, the result may be sub-optimal, in that the meniscus may not be properly aligned to the tibial plane. Also, particularly with the keyhole technique, breaks occur at an undesirable frequency either in the insert or the keyhole during insertion.
Surgeons have also been known to insert the xenograft or allograft meniscus implants by making a slot in the tibia and fitting a rectangular donor bone section into the slot. However, these operations are conducted without instruments specifically designed for this procedure.
The present invention discloses a technique and instrumentation with which to carry out meniscal transplants more effectively and efficiently. Thus, one advantage of the present invention is to improve the quality and long-term results of meniscal transplants by improving the accuracy and stability of the meniscus placement. Another advantage of the present invention is improving the ease of the procedure through the use of specific instruments and through the use of a specific procedure in which a pre-shaped implant may be lodged at an implant site of easily and precisely created and reproduced geometry. These improvements result in less time spent custom-fitting a meniscus implant, and in a more stable implant.
The present invention presents an advance in the method of insertion of an allograft or artificial composite (e.g. allograft bone with integrated SIS CMI, etc.) or xenograft meniscus implant to replace a damaged meniscus in a recipient. Embodiments of a method for the insertion are described, and specific instruments used in the method are described. These instruments facilitate an easier and more efficient surgery for meniscus replacement using the insertion method of the present invention.
In one embodiment of a method of this invention, after exposing the tibia superior surface, a linear shallow groove, or reference slot, is made between and encompassing the anterior and posterior meniscus horn attachments. One way to make the reference slot is with an arthroscopic burr. After a reference slot is formed with a relatively straight and flat bottom, a depth gauge is placed into the reference slot. The distance between the top edges of the gauge at anterior and posterior points, relative to the walls of the groove at these points, are compared. If these are not evenly aligned, such that the same gap exists from front to back between the top of the depth gauge and the top of the reference slot, the gauge is removed and the bone material causing high spot(s) and mal-alignment in the slot is removed, for example, with an arthroscopic burr. This assessment with the depth gauge, and the additional removal of material, are repeated until a groove exists that has a level bottom angled parallel to the tibial slope.
The depth gauge is then re-inserted into the groove, and preferably is stabilized in position, at least partly, by a distal section of the gauge that extends downward over the posterior end of the tibia and purchases onto the posterior margin of the tibia with one tooth, or like means. With the gauge so positioned in the groove, the gauge""s anterior to posterior (xe2x80x9cAPxe2x80x9d) xe2x80x9cliexe2x80x9d mimics that of the tibial slope. A drill guide is placed over the depth gauge at its anterior end. The drill guide is used to position and properly angle a drill bit, which forms a hole for a guide pin. Once the guide pin is set into that hole in the tibia, the guide pin is used as a reference for one of several means to create a slot between the guide pin upward to the reference slot. Once the slot is formed, a sized bone bridge integral with the replacement meniscus (where the horns of said meniscus are attached at the bone bridge""s superior surface) is slid into the slot. As will be described herein, a bone bridge is a segment of donor bone that includes the attachment horns of the meniscus from said donor, and which has been sized to fit the slot in the recipient""s tibia. After alignment of the bone bridge, a pin, screw, suture, or other attaching means stabilizes the bone bridge with the tibia.
In another embodiment, the present invention is directed to a kit for use in a meniscal transplant (implant). In its broadest aspect, the kit comprises a bone bridge sizer; and instructions for use of said bone bridge sizer to cut a bone bridge of a meniscus implant. In one embodiment, the above-described kit also includes a tool to size a slot in a tibia bone, the tool being selected from the group consisting of a slot sizer, a rasp, and a box chisel. In yet another embodiment, the kit of the present invention includes a drill pin and a cannulated drill bit sized to fit over the drill pin. In a further embodiment, the kit comprising a bone bridge sizer and instructions also includes at least one pre-sized meniscus implant.
Additional objects, advantages, and novel features of the invention are set forth in the description which follows, from which such advantages will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention according to this disclosure. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims and equivalents thereof.